Work machine and method of controlling work machine

ABSTRACT

Occurrence of a skid due to revolution of a revolving unit is suppressed. A work machine includes a traveling unit, a revolving unit revolvably mounted on the traveling unit, and a controller that controls operations of the work machine. The controller determines whether or not a skid of the traveling unit has occurred in a revolving operation of the revolving unit during an automatic operation of the work machine. When the controller determines that the skid has occurred, it performs processing for weakening rotational inertial force generated in the revolving operation.

TECHNICAL FIELD

The present disclosure relates to a work machine and a method of controlling a work machine.

BACKGROUND ART

In connection with an excavator, Japanese Patent Laying-Open No. 2019-7173 (PTL 1) illustrates, as movements of the excavator unintended by an operator, a forward dragging movement and a rearward dragging movement in spite of absence of an operation by the operator for a traveling unit, the forward dragging movement being a movement that the excavator is dragged forward by reaction force of excavation, the rearward dragging movement being a movement that the excavator is dragged rearward by reaction force from the ground in a leveling work.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Laying-Open No. 2019-7173

SUMMARY OF INVENTION Technical Problem

The literature discloses that the movement of the excavator unintended by the operator is caused by a movement of an attachment, that is, a boom, an arm, and a bucket, and that the unintended movement can be suppressed by controlling the attachment. Specifically, it is disclosed that the dragging movement of the excavator can be suppressed by correcting a movement of a boom cylinder which is a hydraulic actuator that drives the boom.

In an excavator including a traveling unit and a revolving unit revolvably mounted on the traveling unit, occurrence of a skid of the traveling unit in revolution of the revolving unit with respect to the traveling unit is desirably suppressed from a point of view of efficiency in works. The literature, however, is silent about such a point of view.

The present disclosure provides a work machine and a method of controlling the work machine capable of achieving suppression of occurrence of a skid due to revolution of a revolving unit.

Solution to Problem

According to the present disclosure, a work machine including a traveling unit, a revolving unit revolvably mounted on the traveling unit, and a controller that controls operations of the work machine is provided. The controller determines whether or not a skid of the traveling unit has occurred in a revolving operation of the revolving unit during an automatic operation of the work machine. When the controller determines that the skid has occurred, the controller performs processing for weakening rotational inertial force generated in the revolving operation.

Advantageous Effects of Invention

According to the present disclosure, occurrence of a skid due to revolution of a revolving unit can be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of appearance of a hydraulic excavator based on an embodiment.

FIG. 2 is a diagram showing overview of a system configuration of the hydraulic excavator based on the embodiment.

FIG. 3 is a diagram showing a configuration for controlling revolution of a revolving unit.

FIG. 4 is a block diagram showing a partial electrical configuration of the hydraulic excavator based on the embodiment.

FIG. 5 is a block diagram showing a functional configuration of a controller.

FIG. 6 is a schematic diagram showing a revolving operation of the hydraulic excavator for ejection of soil onto a dump truck.

FIG. 7 is a schematic diagram showing a state of occurrence of a skid of the hydraulic excavator during deceleration in revolution.

FIG. 8 is a flowchart showing a flow of processing when a skid occurs in the hydraulic excavator during deceleration in revolution.

FIG. 9 shows a graph for illustrating first processing for weakening rotational inertial force generated during deceleration in revolution.

FIG. 10 is a schematic diagram for illustrating second processing for weakening rotational inertial force generated during deceleration in revolution.

FIG. 11 is a schematic diagram for illustrating third processing for weakening rotational inertial force generated during deceleration in revolution.

FIG. 12 is a schematic diagram of a system including the hydraulic excavator.

DESCRIPTION OF EMBODIMENTS

An embodiment will be described hereinafter with reference to the drawings. In the description below, the same elements have the same reference characters allotted and their labels and functions are also the same. Therefore, detailed description thereof will not be repeated.

FIG. 1 is a diagram of appearance of a hydraulic excavator 100 based on an embodiment. As shown in FIG. 1, in the present example, hydraulic excavator 100 will mainly be described by way of example as a work machine.

Hydraulic excavator 100 includes a main body 1 and a hydraulically operated work implement 2. Main body 1 includes a revolving unit 3 and a traveling unit 5. Traveling unit 5 includes a pair of crawler belts 5Cr and a travel motor 5M. Travel motor 5M is provided as a drive source for traveling unit 5. Travel motor 5M is a hydraulically operated hydraulic motor.

When hydraulic excavator 100 operates, traveling unit 5 or more specifically crawler belt 5Cr is in contact with the ground. Traveling unit 5 can travel on the ground as crawler belts 5Cr rotate. Traveling unit 5 may include wheels (tires).

Revolving unit 3 is arranged on traveling unit 5 and supported by traveling unit 5. Revolving unit 3 is mounted on traveling unit 5 as being revolvable with respect to traveling unit 5, around an axis of revolution RX. Revolving unit 3 includes a cab 4. A driver (operator) of hydraulic excavator 100 rides on cab 4 and steers hydraulic excavator 100. Cab 4 is provided with an operator's seat 4S where an operator sits. The operator can operate hydraulic excavator 100 in cab 4. In cab 4, the operator can operate work implement 2, can perform an operation to revolve revolving unit 3 with respect to traveling unit 5, and can perform an operation to travel hydraulic excavator 100 by means of traveling unit 5.

Revolving unit 3 includes an engine compartment 9 accommodating an engine and a counterweight provided in a rear portion of revolving unit 3. In engine compartment 9, an engine 31 and a hydraulic pump 33 which will be described later are arranged.

In revolving unit 3, a handrail 19 is provided in front of engine compartment 9. An antenna 21 is provided in handrail 19. Antenna 21 is, for example, an antenna for global navigation satellite systems (GNSS). Antenna 21 includes a first antenna 21A and a second antenna 21B provided in revolving unit 3 as being distant from each other in a direction of a width of a vehicle.

Work implement 2 is mounted on and supported by revolving unit 3. Work implement 2 includes a boom 6, an arm 7, and a bucket 8. Boom 6 is pivotably coupled to revolving unit 3. Arm 7 is pivotably coupled to boom 6. Bucket 8 is pivotably coupled to arm 7. Bucket 8 includes a plurality of blades. A tip end of bucket 8 is referred to as a cutting edge 8 a.

Bucket 8 does not have to include a blade. The tip end of bucket 8 may be formed from a steel plate in a straight shape.

A base end of boom 6 is coupled to revolving unit 3 with a boom pin 13 being interposed. A base end of arm 7 is coupled to a tip end of boom 6 with an arm pin 14 being interposed. Bucket 8 is coupled to a tip end of arm 7 with a bucket pin 15 being interposed.

In the present embodiment, positional relation among components of hydraulic excavator 100 will be described with work implement 2 being defined as the reference.

Boom 6 of work implement 2 pivots with respect to revolving unit 3, around boom pin 13 provided at the base end of boom 6. Movement of a specific portion of boom 6 which pivots with respect to revolving unit 3, for example, the tip end of boom 6, leaves a trace in an arc shape, and a plane including the arc is specified. When hydraulic excavator 100 is planarly viewed, the plane is represented as a straight line. A direction of extension of this straight line is defined as a fore/aft direction of main body 1 of hydraulic excavator 100 or revolving unit 3, and it is hereinafter also simply referred to as the fore/aft direction. A lateral direction (a direction of a vehicle width) of main body 1 of hydraulic excavator 100 or a lateral direction of revolving unit 3 is orthogonal to the fore/aft direction in a plan view, and it is hereinafter also simply referred to as the lateral direction. An upward/downward direction of a vehicular main body or an upward/downward direction of revolving unit 3 refers to a direction orthogonal to the plane defined by the fore/aft direction and the lateral direction, and it is also simply referred to as the upward/downward direction below.

A side where work implement 2 protrudes from main body 1 of hydraulic excavator 100 in the fore/aft direction is the fore direction and a direction opposite to the fore direction is the aft direction. A right side and a left side of the lateral direction when one faces front are the right direction and the left direction, respectively. A side in the upward/downward direction where the ground is located is defined as a lower side and a side where the sky is located is defined as an upper side.

The fore/aft direction refers to a fore/aft direction of an operator who sits at operator's seat 4S in cab 4. A direction in which the operator sitting at operator's seat 4S faces is defined as the fore direction and a direction behind the operator who sits at operator's seat 4S is defined as the aft direction. The lateral direction refers to a lateral direction of the operator who sits at operator's seat 4S. A right side and a left side at the time when the operator sitting at operator's seat 4S faces front are defined as the right direction and the left direction, respectively. The upward/downward direction refers to the upward/downward direction of the operator who sits at operator's seat 4S. A foot side of the operator who sits at operator's seat 4S is referred to as the lower side and a head side is referred to as the upper side.

Boom 6 can pivot around boom pin 13. Arm 7 can pivot around arm pin 14. Bucket 8 can pivot around bucket pin 15. Each of arm 7 and bucket 8 is a movable member movable on a tip end side of boom 6. Boom pin 13, arm pin 14, and bucket pin 15 extend in the lateral direction.

Work implement 2 includes a boom cylinder 10, an arm cylinder 11, and a bucket cylinder 12. Boom cylinder 10 drives boom 6. Arm cylinder 11 drives arm 7. Bucket cylinder 12 drives bucket 8. Each of boom cylinder 10, arm cylinder 11, and bucket cylinder 12 is implemented by a hydraulic cylinder driven with hydraulic oil.

Bucket cylinder 12 is attached to arm 7. As bucket cylinder 12 extends and contracts, bucket 8 pivots with respect to arm 7. Work implement 2 includes a bucket link. The bucket link couples bucket cylinder 12 and bucket 8 to each other.

A controller 26 is mounted on hydraulic excavator 100. Controller 26 controls operations of hydraulic excavator 100. Details of controller 26 will be described later.

FIG. 2 is a block diagram showing a system configuration of hydraulic excavator 100 based on the embodiment. As shown in FIG. 2, hydraulic excavator 100 includes controller (main controller) 26, engine 31, hydraulic pump 33, a tank 35, a main valve 40, and a revolution motor 3M.

The system shown in FIG. 2 is configured such that hydraulic oil delivered from hydraulic pump 33 as a result of drive of hydraulic pump 33 by engine 31 is supplied to various hydraulic actuators through main valve 40. As application and release of a hydraulic pressure to and from the hydraulic actuator is controlled, an operation by work implement 2, revolution of revolving unit 3, and a traveling operation by traveling unit 5 are controlled. The hydraulic actuator includes boom cylinder 10, arm cylinder 11, bucket cylinder 12, and revolution motor 3M as well as travel motor 5M shown in FIG. 1. Revolution motor 3M is provided as a drive source that revolves revolving unit 3.

Engine 31 is, for example, a diesel engine. An engine controller 36 controls operations of engine 31. As engine controller 36 controls an amount of fuel injected into engine 31, output from engine 31 is controlled. Engine 31 includes a driveshaft for coupling to hydraulic pump 33.

Hydraulic pump 33 supplies hydraulic oil to be used for drive of work implement 2 and revolution of revolving unit 3. Hydraulic pump 33 is coupled to the driveshaft of engine 31. As rotational driving force of engine 31 is transmitted to hydraulic pump 33, hydraulic pump 33 is driven. Hydraulic pump 33 is a variable displacement hydraulic pump which includes a swash plate and varies a discharge volume with variation in tilting angle of the swash plate.

In tank 35, oil used by hydraulic pump 33 is stored. Oil stored in tank 35 is suctioned from tank 35 as hydraulic pump 33 is driven, and supplied to main valve 40 through a hydraulic oil path 42.

Main valve 40 is a spool valve that switches a direction of flow of hydraulic oil by movement of a rod-shaped spool. Main valve 40 includes a spool for adjusting an amount of supply of hydraulic oil for each of boom cylinder 10, arm cylinder 11, bucket cylinder 12, and revolution motor 3M. As each spool axially moves, an amount of supply of hydraulic oil to the hydraulic actuator, that is, boom cylinder 10, arm cylinder 11, bucket cylinder 12, and revolution motor 3M, is adjusted. Hydraulic oil is supplied to a hydraulic actuator for activating the same.

Some of oil delivered from hydraulic pump 33 flows into a pilot oil path 50 as being branched from hydraulic oil path 42. Some of oil delivered from hydraulic pump 33 is reduced in pressure in a self-pressure reduction valve 52, and oil reduced in pressure is used as pilot oil. Pilot oil is supplied to main valve 40 for activating the spool of main valve 40.

An EPC valve (electromagnetic proportional control valve) 54 is provided in pilot oil path 50. EPC valve 54 is provided for each spool that adjusts an amount of supply of hydraulic oil for each of boom cylinder 10, arm cylinder 11, bucket cylinder 12, and revolution motor 3M. EPC valve 54 regulates a hydraulic pressure of pilot oil (pilot hydraulic pressure) based on a control signal (EPC current) from controller 26. EPC valve 54 is controlled based on a control signal from controller 26.

EPC valve 54 regulates a pilot hydraulic pressure of pilot oil supplied to each of a pair of pressure reception chambers of main valve 40 to adjust an amount of supply of hydraulic oil to be supplied to the hydraulic actuator through main valve 40. Main valve 40 regulates a direction of flow and a flow rate of hydraulic oil supplied to each hydraulic actuator. As supply of hydraulic oil to each hydraulic actuator is controlled, output of each hydraulic actuator is controlled. Operations of work implement 2 and revolving operations of revolving unit 3 are thus controlled.

FIG. 3 is a diagram showing a configuration for controlling revolution of revolving unit 3. Hydraulic oil path 42 through which hydraulic oil used for revolution of revolving unit 3 with respect to traveling unit 5 flows includes a supply oil path 43 through which hydraulic oil to be supplied to revolution motor 3M flows and a discharge oil path 44 through which hydraulic oil to be discharged from revolution motor 3M flows. Supply oil path 43 is provided with hydraulic pump 33 and a supply throttle 61. Discharge oil path 44 is provided with a discharge throttle 62. Discharge throttle 62 is variable in opening area. By changing an opening area of discharge throttle 62, a flow rate of hydraulic oil that flows through discharge oil path 44 can be controlled.

Main valve 40 shown in FIG. 3 includes a revolution spool 41 that adjusts an amount of supply of hydraulic oil to revolution motor 3M. Supply throttle 61 and discharge throttle 62 are included in revolution spool 41.

A relief valve 66 is provided in a branch line branched from discharge oil path 44 between revolution motor 3M and discharge throttle 62. Relief valve 66 has an input port connected to discharge oil path 44 and has an output port connected to the tank. When a pressure of hydraulic oil that flows out of revolution motor 3M through discharge oil path 44 is equal to or higher than a relief pressure, relief valve 66 is opened and some of hydraulic oil in discharge oil path 44 passes through relief valve 66 to flow to the tank. The flow of hydraulic oil in hydraulic oil path 42 is normally controlled such that the pressure of hydraulic oil in discharge oil path 44 is lower than the relief pressure.

A deceleration in revolution of revolving unit 3, that is, an amount of reduction in revolution speed per unit time, is controlled by using discharge throttle 62. The EPC valve (FIG. 2) that has received a control signal from controller 26 regulates a pilot hydraulic pressure by adjustment of opening thereof. Revolution spool 41 moves in an axial direction in accordance with the pilot hydraulic pressure. Discharge throttle 62 is varied in opening area in accordance with an amount of movement of revolution spool 41.

By decreasing the opening area of discharge throttle 62, the pressure of hydraulic oil in discharge oil path 44 on a discharging side increases and obtained braking force increases. The deceleration of revolving unit 3 thus increases and revolving unit 3 abruptly decelerates in a short period of time. By increasing the opening area of discharge throttle 62, the pressure of hydraulic oil in discharge oil path 44 on the discharging side is lowered and obtained braking force decreases. The deceleration of revolving unit 3 is thus lowered and revolving unit 3 gently decelerates.

FIG. 4 is a block diagram showing a partial electrical configuration of hydraulic excavator 100 based on the embodiment. As shown in FIG. 4, controller 26 includes a memory 261. Memory 261 stores a program for controlling various operations by hydraulic excavator 100. Controller 26 performs various types of processing for controlling operations by hydraulic excavator 100 based on the program stored in memory 261. Memory 261 is a non-volatile memory and provided as an area for storing necessary data.

Antenna 21 provides a signal in accordance with received radio waves (GNSS radio waves) to a global coordinate operation portion 23. Global coordinate operation portion 23 detects a position of installation of antenna 21 on a global coordinate system. The global coordinate system is a three-dimensional coordinate system based on a reference position set in a work area. The reference position may be a position of a tip end of a reference marker set in the work area.

An inertial measurement unit (IMU) 24 is provided in revolving unit 3. In the present example, IMU 24 is arranged in a lower portion of cab 4. In revolving unit 3, a highly rigid frame is arranged in the lower portion of cab 4. IMU 24 is arranged on that frame. IMU 24 may be arranged lateral to (on the right or left of) axis of revolution RX of revolving unit 3. IMU 24 measures an acceleration of revolving unit 3 in the fore/aft direction, the lateral direction, and the upward/downward direction and an angular velocity of revolving unit 3 around the fore/aft direction, the lateral direction, and the upward/downward direction.

A man-machine interface portion 28 includes an input portion 281 and a display (a monitor) 282. Input portion 281 is operated by an operator. Input portion 281 includes an operation button arranged around display 282. Input portion 281 may include a touch panel. A command signal generated in response to an operation onto input portion 281 is provided to controller 26. Display 282 displays basic information such as an amount of remaining fuel and a coolant temperature and information on operations of hydraulic excavator 100.

Controller 26 transmits a control signal to EPC valve 54. EPC valve 54 is controlled based on a control signal from controller 26. EPC valve 54 regulates a pressure of pilot oil supplied to each spool of main valve 40 as the opening thereof is adjusted based on the control signal provided from controller 26. As each spool moves in the axial direction in accordance with the pilot oil pressure, an amount of supply of hydraulic oil to the hydraulic actuator, that is, boom cylinder 10, arm cylinder 11, bucket cylinder 12, and revolution motor 3M, is adjusted.

As the opening of EPC valve 54 corresponding to revolution spool 41 is adjusted based on the control signal provided from controller 26, the pressure of pilot oil supplied to revolution spool 41 is regulated and revolution spool 41 moves in the axial direction. Discharge throttle 62 adjusts the opening area of hydraulic oil path 42 (discharge oil path 44, FIG. 3) in accordance with an amount of movement of revolution spool 41 to regulate the pressure of hydraulic oil in discharge oil path 44.

Controller 26 transmits a control signal to relief valve 66. Relief valve 66 is controlled based on the control signal from controller 26. Controller 26 provides a control signal that indicates a setting value of a relief pressure to relief valve 66.

FIG. 5 is a block diagram showing a functional configuration of controller 26. As shown in FIG. 5, controller 26 includes a revolving unit position obtaining unit 102, a revolution deceleration setting unit 104, a target excavation amount setting unit 106, and a work-implement-attitude-in-revolution setting unit 108.

Revolving unit position obtaining unit 102 obtains a coordinate with respect to a reference position, of revolving unit 3 on which antenna 21 is mounted, from a result of detection of a position where antenna 21 is provided in a global coordinate system detected by global coordinate operation portion 23 based on GNSS radio waves received at antenna 21. Typically, revolving unit position obtaining unit 102 obtains the coordinate of axis of revolution RX. Revolving unit position obtaining unit 102 obtains an angle of revolution of revolving unit 3 with respect to the ground from a result of measurement of an angular velocity by IMU 24.

Revolution deceleration setting unit 104 sets a deceleration in revolution of revolving unit 3, that is, an amount of reduction in revolution speed per unit time. Controller 26 generates a control signal corresponding to the deceleration in revolution set by revolution deceleration setting unit 104 and provides the control signal to EPC valve 54. By regulating the pressure of pilot oil supplied to revolution spool 41 to move revolution spool 41 in the axial direction, the opening area of discharge throttle 62 is adjusted.

Target excavation amount setting unit 106 sets a target value of an amount of excavation of an object to be excavated such as soil by work implement 2. The target value of the amount of excavation is referred to as a target excavation amount below. Target excavation amount setting unit 106 sets the target excavation amount of the object to be excavated. Controller 26 controls work implement 2 such that the target excavation amount of the object to be excavated is loaded in bucket 8 by generating a control signal corresponding to the target excavation amount set by target excavation amount setting unit 106 and providing the control signal to EPC valve 54.

Work-implement-attitude-in-revolution setting unit 108 sets a position of work implement 2 relative to revolving unit 3 at the time when revolving unit 3 performs a revolving operation. Controller 26 controls work implement 2 to take the set attitude during revolution, by generating a control signal corresponding to the attitude of work implement 2 set by work-implement-attitude-in-revolution setting unit 108 and providing the control signal to EPC valve 54.

FIG. 6 is a schematic diagram showing a revolving operation of hydraulic excavator 100 for ejection of soil onto a dump truck 200. As shown with a curved arrow in FIG. 6 (A), revolving unit 3 revolves with respect to traveling unit 5 around axis of revolution RX (FIG. 1). As shown in FIG. 6 (B), revolving unit 3 stops revolution at a position where it is in such an attitude that work implement 2 faces a platform 202 of dump truck 200. At this position, hydraulic excavator 100 ejects an object to be loaded such as soil that has been loaded in bucket 8 onto platform 202 of dump truck 200. The object to be loaded such as soil that has been loaded in bucket 8 represents an exemplary load carried by work implement 2 in the embodiment.

FIG. 7 is a schematic diagram showing a state of occurrence of a skid of hydraulic excavator 100 during deceleration in revolution. FIG. 7 (A) shows revolution of revolving unit 3 around axis of revolution RX as in FIG. 6 (A). In reduction in revolution speed of revolving unit 3, rotational inertial force caused by inertial moment of revolving unit 3 that revolves is applied to traveling unit 5. When rotational inertial force is larger than maximum static friction force of crawler belts 5Cr against the ground, a skid of traveling unit 5 on the ground occurs. When friction resistance between the ground and crawler belts 5Cr is low such as when the ground with which crawler belts 5Cr are in contact is wet with rain, the skid of traveling unit 5 is likely.

A contact area G shown with a dashed line in FIG. 7 (B) represents the ground with which traveling unit 5 is in contact before revolution of revolving unit 3. As shown with a hollow arrow in FIG. 7 (B), when the skid of traveling unit 5 occurs, crawler belts 5Cr move in a direction of revolution of revolving unit 3 and crawler belts 5Cr are displaced from contact area G. When the skid of traveling unit 5 on contact area G occurs, the entire hydraulic excavator 100 moves with respect to the ground and the position of work implement 2 relative to dump truck 200 is displaced.

When position displacement of hydraulic excavator 100 due to the skid becomes great to such an extent that work implement 2 is displaced from platform 202 of dump truck 200 after revolution of revolving unit 3, load may spill due to displacement of a position of soil ejection onto dump truck 200. When revolving unit 3 is revolved in a reverse direction for preventing load spill, a cycle time becomes longer. Occurrence of the skid thus results in lowering of efficiency in excavation and loading works.

Hydraulic excavator 100 in the embodiment suppresses, in the event of such a skid of traveling unit 5 at the time of revolution of revolving unit 3 during the automatic operation for automatic loading from hydraulic excavator 100 to dump truck 200, occurrence of the skid of traveling unit 5 in next revolution of revolving unit 3. FIG. 8 is a flowchart showing a flow of processing when a skid occurs in hydraulic excavator 100 during deceleration in revolution.

As shown in FIG. 8, initially in step S1, excavation is carried out. Controller 26 controls operations of work implement 2 and revolving unit 3 by transmitting a control signal to EPC valve 54. By moving bucket 8 to an appropriate position for doing excavation works and appropriately operating work implement 2 at that position, an object to be excavated such as soil is excavated by bucket 8 and the object is loaded into bucket 8.

In step S2, revolving unit 3 is revolved. Controller 26 controls operations of work implement 2 and revolving unit 3 by transmitting a control signal to EPC valve 54. Revolving unit 3 revolves by a prescribed angle with respect to traveling unit 5 while a position of work implement 2 relative to revolving unit 3 is maintained or work implement 2 is raised or lowered with the load being loaded in bucket 8. The angle of revolution of revolving unit 3 is automatically set by controller 26 based on the position where the excavation works were done and the position of platform 202 of dump truck 200.

In step S3, the position of revolving unit 3 after revolving unit 3 stopped revolution is obtained. Controller 26, specifically revolving unit position obtaining unit 102 (FIG. 5), obtains the position of revolving unit 3 after revolving unit 3 stopped revolution, based on GNSS radio waves received at antenna 21 and/or a result of measurement of an angular velocity by IMU 24.

In step S4, whether or not traveling unit 5 (crawler belt 5Cr) has skidded on the ground is determined. For example, when the position of axis of revolution RX is varied between before and after revolution in spite of the fact that an operation for travel of traveling unit 5 is not performed, a signal for driving travel motor 5M (FIG. 1) is not transmitted to EPC valve 54, and hence travel motor 5M remains stopped, controller 26 determines that traveling unit 5 has skidded on the ground.

Alternatively, a revolution angle sensor detects an angle of revolution of revolving unit 3 with respect to traveling unit 5 and IMU 24 detects an angle of revolution of revolving unit 3 with respect to the ground. When a difference between the detected angles of revolution is equal to or larger than a prescribed threshold value, controller 26 determines that traveling unit 5 has skidded on the ground.

Alternatively, when a difference between a target angle of revolution automatically set by controller 26 based on the position where excavation works were done and the position of platform 202 of dump truck 200 and an angle of revolution of revolving unit 3 with respect to the ground is equal to or larger than a prescribed threshold value, controller 26 determines that traveling unit 5 has skidded on the ground.

The angle of revolution of revolving unit 3 with respect to the ground may be detected by obtaining an image with a vision sensor mounted on hydraulic excavator 100 and estimating a position and an attitude of hydraulic excavator 100 by scan matching. The angle of revolution of revolving unit 3 with respect to the ground may be detected based on a difference between azimuth angles of the GNSS before and after revolution.

When traveling unit 5 is determined as having skidded on the ground (YES in step S4), the process proceeds to step S5, and whether or not the number of times of determination as occurrence of the skid is smaller than a threshold value. Controller 26 reads the number of times of determination as occurrence of the skid before determination in immediately preceding step S4 and the threshold value of the number of times of determination as occurrence of the skid stored in memory 261. Controller 26 adds one to the number of times of determination as occurrence of the skid before determination in immediately preceding step S4 and compares the number of times after addition and the threshold value with each other to determine whether or not the number of times after addition is smaller than the threshold value.

When the number of times after addition is determined as being smaller than the threshold value (YES in step S5), the process proceeds to step S6, and controller 26 performs processing for weakening rotational inertial force generated when the speed of revolution of revolving unit 3 with respect to traveling unit 5 is reduced next time.

FIG. 9 shows a graph for illustrating first processing for weakening rotational inertial force generated during deceleration in revolution. FIG. 9 shows a graph showing variation in revolution speed over time on the occurrence of a skid and next time. The abscissa in the graph represents time and the ordinate in the graph represents the revolution speed.

It is assumed that, on the occurrence of the skid, a revolution speed ω is maintained from time 0 to time T1, deceleration starts at time T1, and the revolution speed is reduced to a revolution speed 0 at time T2. In this case, in next revolution, with the speed being the same at co at time 0, in order to reduce the speed to revolution speed 0 at identical time T2 and to revolve revolving unit 3 by a target angle of revolution, time to start deceleration is set to time T0 before time T1.

By advancing timing to start deceleration in revolution in next reduction in revolution speed after determination as occurrence of the skid, an amount of reduction in revolution speed per unit time is made smaller than that on the occurrence of the skid. By reducing the deceleration in deceleration in revolution, rotational inertial force is weakened. By gently decelerating revolving unit 3, occurrence of the skid is suppressed. By setting rotational inertial force to be weaker than maximum static friction force of crawler belts 5Cr against the ground, occurrence of the skid can be prevented.

An amount of reduction in revolution speed can be controlled by using discharge throttle 62 of revolution spool 41 within main valve 40 shown in FIG. 3. The pressure of hydraulic oil in discharge oil path 44 between revolution motor 3M and discharge throttle 62 is controlled before reaching the relief pressure of relief valve 66. When the pressure of hydraulic oil in discharge oil path 44 downstream from revolution motor 3M is high, resistance against rotation of revolution motor 3M becomes high, which is applied as a brake to stop rotation of revolution motor 3M.

Under the control of the opening of EPC valve 54 by controller 26, the pressure of pilot oil supplied to revolution spool 41 is regulated and the opening area of discharge throttle 62 is varied. By controlling discharge throttle 62 to open, resistance against a flow of hydraulic oil that passes through discharge throttle 62 is lowered. The pressure of hydraulic oil in discharge oil path 44 between revolution motor 3M and discharge throttle 62 is lowered.

As the pressure of hydraulic oil in discharge oil path 44 downstream from revolution motor 3M is lowered, braking force applied to revolution motor 3M is weakened and the amount of reduction in revolution speed can be decreased. Therefore, by opening discharge throttle 62, the amount of reduction in revolution speed per unit time can be decreased.

Alternatively, the amount of reduction in revolution speed can be controlled by using relief valve 66 shown in FIG. 3. When a large setting value of the relief pressure of relief valve 66 is set, the deceleration of revolution increases. When a small setting value of the relief pressure of relief valve 66 is set, the deceleration of revolution decreases. Then, when the skid of traveling unit 5 occurs, the setting value of the relief pressure in next reduction in speed of revolution of revolving unit 3 with respect to traveling unit 5 may be controlled to be set to be smaller.

FIG. 10 is a schematic diagram for illustrating second processing for weakening rotational inertial force generated during deceleration in revolution. FIG. 10 illustrates bucket 8 and load carried in bucket 8, which is typically an object to be excavated such as soil that has been loaded in bucket 8 in excavation works.

It is assumed that, on the occurrence of the skid, load in load amount P1 was carried in bucket 8 and an amount of load carried by work implement 2 was set to load amount P1. In this case, target excavation amount setting unit 106 changes setting of a next target excavation amount to an amount smaller than a current target excavation amount. An amount of load to be carried by work implement 2 is set to a load amount P2 smaller than load amount P1. By decreasing the amount of load carried by work implement 2, rotational inertial force in reduction in revolution speed is weakened. Occurrence of the skid is thus suppressed. By setting rotational inertial force to be weaker than maximum static friction force of crawler belts 5Cr against the ground, occurrence of the skid can be prevented.

FIG. 11 is a schematic diagram for illustrating third processing for weakening rotational inertial force generated during deceleration in revolution. FIG. 11 illustrates a schematic diagram of hydraulic excavator 100 viewed from the left. Revolving unit 3 is revolvably mounted on traveling unit 5 around axis of revolution RX. Work implement 2 is attached to revolving unit 3 as being movable relatively to revolving unit 3. Load P has been loaded in bucket 8.

As compared with the attitude of work implement 2 on the occurrence of the skid, in next revolution, work implement 2 is closer to axis of revolution RX which is the center of revolution of revolving unit 3. By setting a distance from axis of revolution RX to work implement 2 which is typically a distance from axis of revolution RX to bucket 8 in which load P is loaded by setting work implement 2 to a folded position in revolution of revolving unit 3, rotational inertial force in reduction in revolution speed is weakened. Occurrence of the skid is thus suppressed. By setting rotational inertial force to be weaker than maximum static friction force of crawler belts 5Cr against the ground, occurrence of the skid can be prevented.

Thus, when the skid of traveling unit 5 on the ground (contact area G, FIG. 7) occurs, generated rotational inertial force is weakened in next reduction in revolution speed of revolving unit 3 so that occurrence of the skid due to revolution of revolving unit 3 can be suppressed. Then, the process ends (“end” in FIG. 8).

When the number of times of determination as occurrence of the skid is determined as being equal to or larger than the threshold value in determination in step S5 in FIG. 8 (NO in step S5), the process proceeds to step S7 and the automatic operation is stopped. When an event of occurrence of the skid of traveling unit 5 is repeated again in next revolution after processing for weakening rotational inertial force in step S6 and the number of times of the event reaches the threshold value, controller 26 stops the automatic operation of hydraulic excavator 100. In order to avoid such a trouble as failure in obtaining target work efficiency or instability of the attitude of hydraulic excavator 100 due to repeated occurrence of the skid, the automatic operation of hydraulic excavator 100 is stopped. Then, the process ends (“end” in FIG. 8).

An integer not smaller than one is set as the threshold value of the number of times of determination as occurrence of the skid. This threshold value may be stored in advance in memory 261. A setting value of the threshold value may be provided to controller 26 by an operation by an operator onto input portion 281 in man-machine interface portion 28 (FIG. 4).

When traveling unit 5 is not determined as having skidded on the ground in determination in step S4 (NO in step S4), processing for weakening rotational inertial force is not performed or processing for stopping the automatic operation is not performed either, and the process ends as it flows (“end” in FIG. 8).

When processing for weakening rotational inertial force is performed in step S6 and when processing for stopping the automatic operation is performed in step S7, controller 26 may notify an operator that such processing was performed. In addition, the controller may notify the operator that the skid has occurred in revolution of revolving unit 3 and may invite the operator to move to a worksite where the skid is less likely. This notification may be given by showing the notification on display 282 (FIG. 4), using another apparatus for visual notification to the operator such as an indicator, or using an apparatus that gives audio notification to the operator such as a buzzer or a speaker.

An example in which the number of times of determination as occurrence of the skid is used for determination as to whether or not to stop the automatic operation is described with reference to step S7. Instead of this example, the automatic operation may be stopped when an amount of skid exceeds a threshold value. When the amount of skid is large, a vehicular body may become unstable by a single occurrence of skid. By using the amount of skid for determination as to whether or not to stop the automatic operation, an event of instability of the vehicular body can more reliably be avoided.

In the description of the embodiment above, an example in which hydraulic excavator 100 includes controller 26 and controller 26 mounted on hydraulic excavator 100 automatically controls operations of work implement 2 is described. The controller that controls operations of work implement 2 does not necessarily have to be mounted on hydraulic excavator 100.

FIG. 12 is a schematic diagram of a system including hydraulic excavator 100.

An external controller 260 provided separately from controller 26 mounted on hydraulic excavator 100 may configure a system that controls operations of work implement 2. Controller 260 may be arranged at the worksite of hydraulic excavator 100 or a remote location distant from the worksite of hydraulic excavator 100.

Control for suppressing occurrence of the skid in next reduction in revolution speed in the event of occurrence of the skid is described in the embodiment. Control for reducing the deceleration in deceleration in revolution described with reference to FIG. 9 and control for bringing work implement 2 closer to the axis of revolution described with reference to FIG. 11 are applicable without being limited to timing of next deceleration in revolution. For example, when a skid is sensed during automatic revolution, work implement 2 may be brought closer to axis of revolution RX immediately after sensing of the skid or an amount of reduction in revolution speed per unit time may be decreased immediately after sensing of the skid to thereby weaken rotational inertial force.

Measures against the skid in deceleration in revolution of revolving unit 3 are described in the embodiment. Control for reducing load carried in bucket 8 described with reference to FIG. 10 and control for bringing work implement 2 closer to axis of revolution RX described with reference to FIG. 11 are similarly effective also as measures against occurrence of the skid of traveling unit 5 in acceleration in revolution of revolving unit 3. Therefore, by performing processing for weakening rotational inertial force on the occurrence of the skid of traveling unit 5 at the time of fluctuation in revolution speed of revolving unit 3, occurrence of the skid can be suppressed.

Measures against the skid at the time of fluctuation in revolution speed of revolving unit 3 are described in the embodiment. Control for reducing load carried in bucket 8 described with reference to FIG. 10 and control for bringing work implement 2 closer to axis of revolution RX described with reference to FIG. 11 are similarly effective also as measures against occurrence of the skid of traveling unit 5 while revolving unit 3 is revolving at a constant revolution speed. Therefore, by performing processing for weakening rotational inertial force on the occurrence of the skid of traveling unit 5 in the revolving operation of revolving unit 3, occurrence of the skid can be suppressed.

Though hydraulic excavator 100 is described by way of example of a work machine in the embodiment, the work machine to which the concept of the present disclosure is applicable may be a mechanical ultra large rope excavator that is not hydraulically driven and an electric excavator driven by an electric motor.

It should be understood that the embodiment disclosed herein is illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims rather than the description above and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

REFERENCE SIGNS LIST

-   -   1 main body; 2 work implement; 3 revolving unit; 3M revolution         motor; 5 traveling unit; 5Cr crawler belt; 5M travel motor; 6         boom; 7 arm; 8 bucket; 8 a cutting edge; 9 engine compartment;         10 boom cylinder; 11 arm cylinder; 12 bucket cylinder; 21         antenna; 21A first antenna; 21B second antenna; 23 global         coordinate operation portion; 24 IMU; 26, 260 controller; 28         man-machine interface portion; 31 engine; 33 hydraulic pump; 35         tank; 36 engine controller; 40 main valve; 41 revolution spool;         42 hydraulic oil path; 43 supply oil path; 44 discharge oil         path; 50 pilot oil path; 52 self-pressure reduction valve; 54         EPC valve; 61 supply throttle; 62 discharge throttle; 66 relief         valve; 100 hydraulic excavator; 102 revolving unit position         obtaining unit; 104 revolution deceleration setting unit; 106         target excavation amount setting unit; 108         work-implement-attitude-in-revolution setting unit; 200 dump         truck; 202 platform; 261 memory; 281 input portion; 282 display;         G contact area; P load; P1, P2 load amount; RX axis of         revolution 

1. A work machine comprising: a traveling unit; a revolving unit revolvably mounted on the traveling unit; and a controller that controls operations of the work machine, wherein the controller determines whether a skid of the traveling unit has occurred in a revolving operation of the revolving unit during an automatic operation of the work machine, and when the controller determines that the skid has occurred, the controller performs processing for weakening rotational inertial force generated in the revolving operation.
 2. The work machine according to claim 1, wherein when a speed of revolution of the revolving unit with respect to the traveling unit is varied, the controller performs the processing for weakening the rotational inertial force by reducing an amount of variation in revolution speed per unit time.
 3. The work machine according to claim 1, further comprising a work implement mounted on the revolving unit, wherein the controller performs the processing for weakening the rotational inertial force by bringing the work implement closer to a center of revolution of the revolving unit.
 4. The work machine according to claim 1, further comprising a work implement mounted on the revolving unit, wherein the work implement includes a bucket for excavation of an object to be excavated, the controller includes a target excavation amount setting unit that sets a target excavation amount of the object to be excavated, and when the controller determines that the skid of the traveling unit has occurred, the controller performs processing for weakening next rotational inertial force by changing setting of a next target excavation amount to an amount smaller than a current target excavation amount.
 5. The work machine according to claim 1, wherein when the controller determines that the skid of the traveling unit has occurred after the controller performed the processing for weakening the rotational inertial force, the controller stops the automatic operation of the work machine.
 6. A method of controlling a work machine, the work machine including a traveling unit and a revolving unit revolvably mounted on the traveling unit, the method comprising: determining whether a skid of the traveling unit has occurred in a revolving operation of the revolving unit during an automatic operation of the work machine; and performing processing for weakening rotational inertial force generated in the revolving operation when it is determined in the determining that the skid has occurred. 